1. Field of the Invention
The field of the present invention is synchro mechanisms for use in a multi-stage type transmission, and more particularly, synchro mechanisms designed to permit an outer member such as a gear relatively rotatably carried on an input or output shaft to be brought into engagement with an inner member which rotates in unison with the shaft.
2. Description of the Prior Art
There is a conventionally known roller synchro mechanism described in U.S. Pat. No. 4,817,451.
This roller synchro mechanism has a structure in which a plurality of rollers are disposed between a roller abutment surface formed at the inner periphery of a gear relatively rotatably carried on a rotary shaft and cam grooves provided on the outer periphery of an inner cam secured to the rotary shaft, and a dowel formed on a sleeve is adapted to be engaged into and disengaged from a dowel-admission groove made in a side of a retainer which retains the rollers while permitting their slight movement in a radial direction. In a state of the dowel of the sleeve being in engagement in the dowel-admission groove in the retainer, the rollers are fitted into the cam grooves and moved radially inwardly away from the roller abutment surface formed on the gear, thereby releasing engagement between the rotary shaft and the gear. On the other hand, in a state of the dowel of the sleeve being removed from the dowel-admission groove in the retainer, the rollers are urged radially outwardly by the cam grooves to bear against the roller abutment surface, thereby causing the rotary shaft and the gear to be brought into integral engagement with each other.
However, the above prior art roller synchro mechanism has a disadvantage of an increased thickness of the retainer, resulting in an increased axial dimension of the entire roller synchro mechanism, because the dowel-admission grooves in the retainer and the roller-retaining holes are juxtaposed axially. In addition, the inner cam, the rollers and the retainer are contained in a projection formed on a side of the gear, resulting in an increased thickness of the gear. This also causes an increase in axial dimension of the entire roller synchro mechanism.
The retainer used in the above prior art roller synchro mechanism is held merely in a loosely fitted manner on the roller abutment surface of the gear and for this reason, there is a possiblity that when the dowel of the sleeve is removed from the dowel-admission groove in the retainer to effect the engagement between the gear and the rotary shaft, the gear and the retainer may slip causing a time lag until engagement is achieved. Further, roller-retaining grooves in a retainer require an extremely high accuracy in machining, but the retainer in the above prior art roller synchro mechanism is comprised of a single component and hence, has a disadvantage that machining of the roller-retaining grooves having a non-circular section is difficult and requires a high cost.